1. Technical Field
The present invention relates to a fluid conveying device which ejects a small volume of fluid at a low speed, and a driving method for this fluid conveying device.
2. Related Art
A peristaltic pump is traditionally known as a device for conveying a liquid at a low speed. In the peristaltic pump, plural rollers are arranged on the same circumference on a rotor, and a tube is arranged to surround the outer circumference of the rotor. As the rotor is rotated, the tube is squeezed in a liquid flowing direction by the plural rollers. The squeezing position is moved gradually, thus ejecting the liquid (for example, see JP-A-2004-92537).
In the case of ejecting a minuscule volume of fluid, the rotor in the peristaltic pump is rotated by being driven and stopped intermittently. Therefore, a pulsating current unique to the peristaltic pump is generated and the ejection volume becomes irregular. Thus, according to JP-A-2004-92537, the ejection volume at each of intermittent driven and stop positions of the rotor is measured and stored in advance, then the sum of the ejection volumes corresponding to the rotation angles of the rotor is calculated, and the rotation angle of the rotor is controlled according to a required total ejection volume.
However, the peristaltic pump has such a characteristic that the ejection volume changes each at rotation angle of the rotor in the process of liquid flowing. Therefore, it is necessary to finely divide the rotation angle of the rotor, measure and store the ejection volume at each of the divided angles, and calculate the sum of the ejection volumes at each angle every time the rotation of the rotor proceeds. Therefore, there is a problem that a rotor rotation angle control unit, including a CPU which is charge of the calculation and a memory for storing and rewriting the rotation angle of the rotor and the result of calculating the ejection volume, bears a heavy load.
JP-A-2004-92537 also discloses that data of the total ejection volume per turn of the rotor is stored in a memory in advance so that the rotation angle of the rotor is found. However, since the ejection volume fluctuates at each rotation angle of the rotor during one turn of the rotor, there is a problem that an accurate total ejection volume is difficult to grasp.